Prepositioning motor control



1957 c. A. SCHURR EI'AL 2,817,053

PREPOSITIONING MOTOR CONTROL Filed June 24, 1955 3 Sheets-Sheet 1 IN VEN TORS CHARLES ALLAN SCHURR FRANK ALAN MANNERE Dec. 17, 1957 c. A.SCHURR ETAL 2,817,053

PREPOSITIONING MOTOR CONTROL Filed June 24, 1955 s Sheets-Sheet 2 fi.r60

INVENTORS CHARLES ALLAN 5CHLJRR FRANK ALAN MAMNERB Dec. 17, 1957 c. A.scHuRR ETAL 2,817,053

PREPOSITIONING MOTOR CONTROL Filed June 24, 1955 I5 Sheets-Sheet 3 mfi Mm H w E mm m V M m? A d a HR CF Y B 3 E w a M m United States PatentPREPOSITIONING MOTOR CONTROL Charles Allan Schurr, Warrensville Heights,and Frank Alan Manners, Cleveland, Ohio, assignors, by mesneassignments, to Square D Company, Detroit, Mich., a corporation ofMichigan Application June 24, 1955, Serial No. 517,752

Claims. (Cl. 318-490) This invention relates to a control system for anelectric motor, and more particularly to a control system forautomatically predetermining and indicating, between operating periodsof the motor, the number of revolutions to be made by the motor duringits next subsequent operating period. Although not limited to such use,the invention is described herein as applied to the control of ascrew-down motor for a metal rolling mill.

in the operation of many rolling mills, it is necessary to repeatedlyvary the spacing of the rolls while reducing a metal piece such as asteel bloom or ingot to a desired size and shape. In so doing the bloomor ingot is passed between the rolls at least once for each spacing.Between the passes, the spacing of the rolls is varied by the screwdownmotor. Motor controllers, known as automatic preset: screw-downcontrollers, have been developed which permit one or more completerolling schedules to be preset thereby rendering the roll spacing foreach pass uniform and proper and not a matter of choice by the operatorduring the reducing operation.

Automatic preset screw-down controllers having differentially drivencontrol elements, such as described and claimed in Wright and WilcoxPatent No. 2,106,965 and in Schurr Patent No. 2,564,284, have been usedextensively in the control of various types of rolling mills in severaldifferent metal-working industries. The speed and accuracy of theseprior controllers is outstanding. There has been a demand, however, fora control system of equal speed and accuracy which permits the operatorto select quickly and accurately the next subsequent roll spacing whilethe metal is between the rolls so that, immediately after the metalleaves the rolls, mere operation of a push button causes the screw-doommotor to rotate until the preselected roll spacing is provided for thenext successive pass. A preselect system, as distinguished from a presetsystem, is particularly suitable for mills handling a large number ofdifferent sizes of blooms or ingots which would require the pro-settingof an excessively large number of rolling schedules if a preset systemwere used.

An object of this invention is to provide an improved preselect electricmotor control system including means for preselecting, between operatingperiods of the motor, any desired number of revolutions to be made bythe motor during its next subsequent operating period so that, shouldthe operator note the need for a change in his usual procedure, he caninstitute it between successive starts of the motor.

Another object is to provide an electric motor control system forindicating, and then automatically controlling, the number ofrevolutions to be made by the motor and including a coarse controlcut-out and a fine control cutout both coupled to the motor through adifferential gear.

Another object is to provide an improved motor control system in which,while the motor is stopped, a means which indicates the position of theapparatus driven by the motor can be adjusted to indicate the nextdesired position of the apparatus and which remains in fixed 2,817,053Patented Dec. 17, 1957 position during movement, by operation of themotor, of the apparatus to that pre-selected position.

Another object is to provide an improved automatic pie-select screw-downcontroller.

Another object is to provide an improved automatic pro-select screw-downcontroller in which an indicating means indicates, selectively, theactual roll spacing at the end of an operation of the motor, and, beforethe next operation of the motor, the desired next subsequent rollspacing to be obtained by such subsequent motor operation, theindicating means being geared to stopping control means which stops thescrew-down motor automatically when the desired next subsequent rollspacing is reached.

Another object ,is to provide an improved preselect screw-downcontroller in which a screw-down motor drives control means whichautomatically stops the screwdown motor when the rolls are at apreselected spacing and in which a roll-spacing-indicating means and thecon trol means can be preset while the screw-down motor is not operatingto indicate and predetermine the next subsequent roll spacing.

In accordance with this invention, a screw-down motor is arranged todrive the main driving shaft or gear of a difierential gear mechanismthrough a synchronous-tie system. One of the shafts driven through thedifferential gearing is coupled to a roll-spacing-indicating meansthrough a second synchronous-tie system and the other of the shafts ofthe differential gearing drives a fine control or vernier cut-out and acoarse control or main cutout in fixed speed relation to each other.When the cutouts reach their respective neutral positions, the screwdownmotor is tie-energized. To preselect the next roll spacing, the cut-outsare driven a predetermined distance from their neutral positions by aset-up motor geared to the differential shaft which is coupled to theindicating means. Thus when the set-up motor is operated to drive thecut-outs, the indicating means is driven to a position where itindicates the next desired roll spacing. Subsequent operation of thescrew-down motor drives the cut outs until both are returned to theirrespective neutral positions at which time the screw-down motor stopsautomatically. During operation of the screw-down motor the dilferentialshaft to the indicating means is self-locked so that the indicatingmeans does not operate and therefore the indicating means gives a trueindication of the actual rollspacing when the screw-down motor stops.

Other objects and advantages will become apparent from the followingdescription wherein reference is made to the drawings, in which:

Fig. 1 is a schematic layout of a portion of the apparatus showing itsrelation to a screw-down motor;

Fig. 2 is a schematic front view of the indicating means;

Fig. 3 is a wiring diagram showing the electrical connections for thesynchronous-tie machines; and

Figs. 4A and 4B together are a complete wiring diagram of the remainderof the control system.

In the wiring diagrams of Fig. 3, 4A, and 413, some of the switchcontacts and their operating windings are shown in convenient physicallocations in the diagrams apart from each other and are also shownoperatively associated with each other. The switch contacts and windingsare referred to by the appropriate reference numeral followed by aletter subscript. In order to simplify the drawing and thereby to makethe invention easily understood certain conventional relays andinterlocking contacts the use of which in similar control systems iswell known have been omitted.

Referring principally to Fig. 1, a screw-down motor 10 which may be aseries-wound direct current machine hav-' ing, as shown in Fig. 4A, anarmature winding 10a and a series field winding 10f is suitably coupledas by gearing 11 to a screw-down mechanism'associated with relativelymovable rolls 12 of a metal-rolling mill" formoving the" rolls towardand away from each other. The rotor of a suitable synchronous-tietransmitter 14 is coupled to a shaft 15 driven through gearing 1-8hythemoto'r10: The transmitter 14 drives'the rotor'of a synchi'onous'tiereceiver 19 having ashaft-ZO-whili drivestthrough' gearing 21 apinion shaft 22 carryingapinion 24"nieshingwith a ring or main drivinggear 25' of an automobiletypedifierential 26 having differential shafts28 and 29 drivin'gly' mounted at any; convenient loc'a'ti differential26, for enam'pl'e, adjacenttdriialster switches to be described.

The indicator 34 may comprise gearing SS which couples the rotor of thereceiver 31 to" a shaft" 36 carrying at its forward end portion a fineor Vernier p'oin'ter 38 associated with a graduated dial 39 (Fig. 2').associated with a gradnated dial 41' is driven by gearing 42 and 43 fromthe shaft 36,. Initlieillustr'ative example, the maximum roll spacing isassumed to be fifteen inches and the gearing is selected so that thepointer 40 makes one revolution while the rolls are moving the fullfifteen inches. One inch increments of the fifteen inch spacing aremarked on the dial 41. The ratio of the geai'ing 42 and 43'is' such thatthe pointer 38 rotates 15 times faster than the pointer and thus thedial 39 is graduated'to show tenths and hundredths of an inch of rollspacing. A rearward extension of the shaft 36 has a knob that. may heused for adjustment of the pointers 38 and: 40 and preferably the statorof the receiver 31 is rotatahle iri the housing 34 to permit accuratecalibration of the indicator: with respect to the spacing of the rolls 12. After calibration, the frame of the receiver 31 islocked'iri'positiori by suitable means (not shown).

Keyed at an intermediate portion of the shaft 28-. is a worm wheel 44meshing with a worm 45. secured to the shaft of a suitable pro-selectingor set-up motor 46-which is shown in Fig. 4Aa's a shunt wound directcurrent machine having an armature winding 46a. and a shunt fieldwinding 46f.

Rigidly secured tothe outer end portion of the shaft- 29 is an arm 48a(Fig. 4B) of a fine control device or Vernier cut-out 48 and keyed at anintermediate portion of the shaft 29 is a worm 49 meshingz with a wormwheel 50 on a shaft 51 coupled to an arm 2a (Fig. 4B) of'a coarsecontrol device or main cut-out 52.. Although the: cut-outs 48 and. 52may be of any. suitabletype and may be cam operated, they are showninFig. 413 as of. the faceplate type. The various contact segmentsof thecut-outs 48 and 52 are identified by the appropriate referencenumeral'followed by a letter subscript and will be further referred toin the description of operation. J

The ratio of the worm 49 and wheel 50 may be any suitable value, but forgreatest accuracy preferably is relatively high, as for example 60-to 1so that six degrees rotation of the arm 52a corresponds to onerevolution of the arm 48a. Further in the. illustrative example, thegearing between the arm -48a and the rolls-12 18 511011 that one inch ofroll travel corresponds'to tworrevolut-ionsa of the arm 48a and thustwelve degrees of rotation; of the arm 52a corresponds to one inch ofroll travel.

When the pinion 24 is driving the ring. gear 25, the shaft 29 rotatesbut the shaft '28'does. not since it is. locked by the worm 44 and wheel45. On; theother hand, when the set-up motor 46 is operated to drive theshaft 28 and A coarse pointer 40' the pinion 24 is not rotating, theshaft 29 rotates at the same speed as the shaft 28 but in the oppositedirection due to action of the differential 26. Thus, in theillustrative example, if the set-up motor is operated to drive theindicator to show a one inch movement of the rolls 12, the arm 48a makestwo revolutions and the arm 52a rotates 12 degrees from its initialposition. If the one inch movement of the rolls is to space the rolls 12further apart, the arms 48a and 52a rotate in one direction from theirneutral position, whereas if the roll movement is to space the rolls 12closer together, the arms 48a and 52a rotate in the opposite direction.

Referring now to Fig. 3, when a knife switch 54 is closed, primarywindings of the synchronous-tie machines 14 and 19 are connected to asuitable source of alternating current indicated by conductors 55. Therotor windings of the machines 14 and 19 are permanently connected together as are those of the synchronous-tie machines 30 and 311.Up'on'closur'e of a master switch shown as a push button 56, the primarywindings of the synchronous-tie machines 30 and 31 are connected to thesource 55 and an operating winding 58w of an electromagnetic relay 58 isenergized causing the relay 58 to move to its operated position. Therelay 58 serves as an interlock between the alternating current portionof the control system shown in Fig. 3 and the direct current portionshown in Fig. 4B and hence the contacts of the relay 58 are shown inFig. 4B. As will become apparent, should the alternating current source55 fail While the system is operating automatically, consequentdeenergization of the relay 58 causes the motor 10 to stop thereby tomaintain synchronism between the rolls 12 and the cut-outs 48 and 52 andthe indicator 34.

Referring now to Fig. 4A, the motors 10 and 46 are arranged to besupplied from a suitable direct current source indicated by the supplyconductors 59 and 60. The armature winding 10a of the screw-down motor10 is arranged to be connected for driving the rolls 12 upwardly uponclosure of a normally open, two-pole, electromagnetic contactor 61 andfor driving the rolls 12 downwardly upon closure of a normally-open,two-pole electromagnetic contactor 62. An operating winding 64w of asuitable spring-applied, electromagnetically released brake (not shown)for the motor 10 may be connected in series with the motor. Anacceleration and plugging controlling resistor 65 also in series withthe motor 10 has portions arranged to be by-passed by normally-open,single-pole, electromagnetic contactors 66, 67, and 68, respectively,the'contactor 66 serving as a plugging contactor during non-automaticoperation of the motor 10. Slowdown of the motor 10 prior to stopping iseffected by an armature shunt circuit including a resistor 69 which isarranged to be connected across the armature 10a upon closure of anormally open, single pole, electromagnetic contactor 70, normally open,single-pole electromagnetic contactors 71 and 72 being provided to varythe effective value of the resistor 69. A normally open, single-pole,electromagnetic contactor 73 serves to connect the motor 10 to thesupply conductor 60.

The set-up motor 46 which may be a fractional horsepower machine isarranged to be reversibly connected to the conductors 59 and 60 througha permanent resistor 74 by selective operation of a normally open,double-pole, electromagnetic forward or up contactor 75 and a normallyopen, double-pole, electromagnetic reverse or down contactor 76.Slowdown of the motor 46 prior to stopping is'effectedby an armatureshunt circuit including a resistor 78 arranged to be connected acrossthe armature 46a by" a normally closed, single-pile, electromagneticcontactor 79. Final slowdown of the motor 46 just prior to stopping isaccomplished by short-circuiting the armature 46a by closure of anormally open, single pole, electromagnetic contactor 80.

Operation of the set-up motor 46 is controlled by a two-positionreversing master switch 81 having contacts 81a through 81d. In the offposition of the master switch 81, the contact 810 is closed andcompletes an energizing circuit for an operating winding 80w of thecontactor 80 from the conductor 59 to the conductor 60. The contact 810is open in all other positions of the master switch 81 and the contacts81a, 81b, and 81d are open in the off position and are closed in thoseother positions where closure is indicated by crosses aligned with thecontacts. In the up positions of the master switch 81, the contact 81ais closed and completes an energizing circuit for an operating Winding75w of the up contactor 75 and in the down positions the contact 81d isclosed and completes an energizing circuit for a winding 76w of the downcontactor 76. The contactor 79 which controls the armature shunt circuitthrough the resistor 78 remains closed in both first positions and openswhen the master switch 81 reaches either one of its second positionssince closure of the contact 81b completes an energizing circuit for anoperating winding 79w of the contactor 79. Thus by operation of themaster switch 81 the motor 46 may be operated at two different speeds ineither direction and stops quickly when the oif point is reached becausethe contactor 80 then closes to short-circuit the armature Winding 46aThe screw-down motor may be operated non-automatically by means of amulti-position, reversing, master switch 82 (Fig. 4B) having contacts82a through 82 The contacts 82b and 82 are closed in the off positionand crosses aligned with the contacts indicate the closed condition ofthe contacts 8211 through 82e in the other positions. When the masterswitch 82 is in any of its up positions, an energizing circuit iscompleted through the contact 82d for an operating winding 61w of the upcontactor 61, and when the master switch 82 is in any of its downpositions, an energizing circuit is completed through the contact 82afor an operating Winding 62w of the down contactor 62. The contact 82cis closed whenever the master switch 82 is in one of its operatingpositions and completes an energizing circuit for an opera-ting winding73w of the contactor 73. When the master switch 82 is in either of itsfirst positions all of the resistor 65 is in series with the motor 10.Upon movement of the master switch 82 to either of its second positions,an energizing circuit is completed through the contact 82b for anoperating winding 66w of the plugging contactor 66 which may also becontrolled by a plugging relay (not shown) in a Well known manner. Uponmovement of the master switch 82 to either of its third positions, anenergizing circuit is completed through the contact 82a and a normallyclosed contact 8411 of a control relay 84 for an operating winding 67wof the contactor 67. After a time delay of an acceleration relay (notshown), an energizing circuit is also completed from the contact 84athrough a normally closed contact 85a of a control relay 85 to anoperating winding 68w of the contactor 68.

It is thus seen that the master switch 82 provides a means to controlthe motor 10 manually, that is, nonautomatically, so as to move therolls 12 any desired distance in opposite directions selectively at anyof three different speeds. This manual operation of the motor 10 can beeffected with alternating current power available or not. Preferably themaster switches 81 and 82 are arranged adjacent to each other and to theindicator 34.

Before the motor 10 can be operated automatically, the system must besynchronized with the indicator 34 set to indicate the exact distancebetween the rolls 12 and with the cut-outs 48 and 52 at their respectiveneutral positions. This is preferably accomplished by removing powerfrom the synchronous-tie machines 30 and 31, operating the motor 10 bymeans of the master switch 82 until the rolls 12 are a predetermineddistance apart, and then operating the set-up motor 46 until the arms48a and 52a are in their respective neutral positions. The knob on theindicator shaft 36 is then used to set the pointers 38 and 40 so thatthey indicate the predetermined roll spacing. Power is then re-appliedto the machines 30 and 31 and to the relay winding 58a. There is atendency for the receiver 31 to rotate slightly when power is re-appliedto thus disturb the setting of the pointers. If this rotation occurs,the stator of the receiver 31 may be turned slightly in the housing 32to compensate for the change in setting and then again locked inposition.

In describing automatic operation of the system, it will be assumed thatthe system has been synchronized as just described, that the gear ratiosare as previously given for the illustrative example, that the rolls 12are exactly five inches apart, and that it is desired to move the rolls12 toward each other 1% inches so that they become 3% inches apart.Since the system is synchronized, the pointers 38 and 40 of theindicator 34 stand so that 5.00 inches is read from the dials 39 and 41.The master switch 82 must be in its oif position during automaticoperation. The push button 56 is closed so that the synchronous-tiemachines 30 and 31 are energized and the relay 58 is in its operatedposition.

The set-up motor 46 is now started in the down direction by manipulationof the master switch 81 and drives the shaft 28 of the differential 26until the pointers 38 and 40 indicate the desired spacing of 3% inches.The master switch 81 is then returned to the OE position and the set-upmotor 46 stops. By the locking action of the worm 44 and worm wheel 45,the pointers 38 and 40 are held in the selected position duringsubsequent operation of the screw-down motor 10. Because of the assumedgear ratios previously mentioned, this operation of the set-up motor 46has driven the Vernier cut-out arm 48a from its neutral position 3%revolutions in a clock-wise direction (Fig. 4B) and the main cut-out arm52a from its neutral position twenty-one degrees in a clock-wisedirection. As soon as the contact arm 52a moved from its neutralposition, a contact bridge 52b on the arm 52a bridged a main contactring 52m and a down contact segment 52d. A circuit was thereby completedfrom the supply conductor 59 through the master switch contact 821, thecontact ring 52m, the contact bridge 525, the contact segment 52d, andan operating winding 86w of a down relay 86 to the supply conductor 60.Consequently a normally closed contact 86b of the relay 86 is now openand isolates an up segment 48a of the vernier cut-out 48 from thecircuit and normally open contacts 86a and 860 of the relay 86 are nowclosed and complete a by-pass circuit to be described around the cut-out48 so that the position of the contact arm 48a is of no consequence atthis time.

When it is desired to operate the screw-down motor 10, a master switchshown as a push button 88 is closed and completes an energizing circuitfor an operating winding 89w of a relay 89 from the conductor 59 throughthe contacts 82f and 58b, the push button 88, and the winding 89w to theconductor 60. A normally open contact 89a of the relay 89 closesimmediately and causes energization of an operating winding 84w of thecontrol relay 84. Consequent closure of a normally open contact 84d ofthe relay 84 completes an energizing circuit for the operating Winding62w of the down contactor 62 from the supply conductor 59 through thecontact 84a, the contacts 86a and 860 of the relay 86, a contact 582 ofthe relay 58, and the winding 62w to the conductor 60. At the same time,closure of a normally open contact 84c of the relay 84 causesenergization of the op erating winding 73w of the contactor 73. Theresultant closure of the contactors 62 and 73 causes the motor 10 to runin the down direction. The plugging portion of the resistor 65 isexcluded because the contactor 66 is closed as a result of energizationof the winding 66w through the contact 82b. An energizing circuit isalso completed for the windings 67w and 68w through the contacts 84d,86a, 58a, and 84b causing sequential closure of the contactors 67 and 68to permit the motor 10 to reach its maximum speed, closing of thecontactor 68 being d ye i a l know imanne p evious y ent ned l ur ilaotac 1-621 oath cpntac cr 62completes with the contact 89 a;abypass;circuitaround the push button $8 which'may now be released. vIif.-,desired, the contacts 89a may be delayed in opening, so that thepush button 88 may be releasedas soon asthe contacts 89:: close.

Operation of the motor 1b in the down direQtion mov the rolls 12 towardeach other and causes theishaft 29 of the differential 26 to drive themain cutaoutarmfizn counter-clockwise towards its neutral .position.Before the arm 52a reaches its neutral position, the contact bridge 52bengages a contact segment 52p thereby to complete an energizing circuitfor an operatinglwinding 91w of a relay 91 provided a knifeswitch 92-isin its upper position. if the knife switch :92-were in its lowerposition, the relay 91 would be operated sooner by en gagement of thecontact bridge "52b .with'a contact segment 5271. Operation of the relay91 causes closure of a contact '91:: which completes anenergizing-circuit tor an operating winding 85w of the relay-85.-,'Consequent opening of the contact 85a of the'relay 85 oauses openingof the contactor 68, and closure ofa contact 8511- of the relay 85causes energization of the operating winding MW of the contactor 70which completes the armature shunt circuit for the motor 10 causing themotor -10-to operate at a slower speed. Thus the knife switch 92 permitsthe starting point-for slowdownof the motor 1 to be adjusted.

Because of the exemplary gear ratios previously mentioned, when the arm52a is three degrees from its neutral position, a contact bridge 4812 onthe arm 48a of the Vernier rheostat 48 engages a contact segment-48d andcompletes a circuit between the segment 48d and the contact ring 48m.When the arm 52a is 2% degrees from its neutral position, the contactbridge 52b leaves the contact segment 52d which deenergizes'the relay 86causing its contacts 36a and 86c to open thereby opening the by-passcircuit around the ernier rheostat 48 and one of the circuits to thewinding 62w. Since the contact bridge 48b has left the contact segment4811, reclosure of the contacts 86b is of no eifect.

Engagement of the contact bridge 48b with the contact segment dlidcompletes a circuit from the conductor 59 through the contact 84d, thecontact ring 48111, the contact bridge 48b, the contact segment 48d,normally closed contacts 9% of an up relay 9.4, and the contacts 53@through the winding 62w to the conductor 60. The contactor e2 thusremains in its closed position and the motor 1d continues to operate inthe down direction driving the contact arm 48a counter-clockwise towardits neutral position. Before the contact arm '48a;reaches its neutralposition, a contact bridge 480 on the arm 48a completes a circuit from acontact segment 48p to a contact segment 481'. This completes a circuitfrom the conductor 59 through the contacts'82f and 58b and the operatingwinding 72w of the armature shunt contactor '72 to the conductor 60. Thecontactor 72 thereupon closes to reduce the efiective value of theresistor'69 in the armature shunt circuit for the motor 10. The motor 10consequently slows down and continues to run at a slower speed. A shorttime later the contact bridge 48b engages a contact segment 4812 tocomplete aicircuit from the contact ring 48m through the brush 48b andthe segment 4812 to the operating winding 71w of the armature shuntcontactor 71 which thereupon closes to reduce further the effectivevalue of the resistor-.69 in the armature shunt circuit for the motor10.

The speed of the motor 10 is now very slow. .When the arm 43a reachesits neutral position the contact bridge 48b leaves the segment 48dcausing opening of the contactor 62. This deenergizes the motor 10,andcauses the friction brake operated by the winding 64w to setwandstop the motor 10. The motor 10 has now driventhe 1';olls, 12 .towardeaehother so that they are now exactly 3% inches :apart as shown by theindicator .34.

Opening of the contactor 62. caused opening of thecontacts 62a intheholding circuit for the time relay 89. After a time interval, therelay 89 opens its contacts 89a causing .deenergization of the relays 84and 85 and the contactor 70. Opening of the relay84 causesdeenergization of the contactors 67 and 73.

If it should now be desired to separate the rolls, the master switch .81is operated to cause the set-up motor 4-6 to. operate in the updirection. This moves the pointers 38 and 40- on the indicator 34 toindicate the desired wider roll spacing and at the same time moves thearms 48a and 52a a comparable distance counter-clockwise. When thepushbutton-88 is now closed, circuits similar to those previously describedare completed except that the contact segment 5214 is first effectiveand the contact segment .4811 later becomes effective instead of thecontact segments 48d and 52a. The up control relay 94 having, inaddition to its normally closed contacts 941'), normally open contacts94!: and 940 operates during separation of the rolls instead of the downrelay 86, and the up contactor 61 closes to cause the motor 10 tooperate in the up direction. An energizing circuit for the winding 61wis completed around the cutout 43 through the. contacts 84a, 94a, 94c,and The contacts 61a instead of the contacts 62a serve to complete thecircuit around the push button 88 while the motor 10 is operating in theup direction.

Itis thus seen that while the motor 10 is stopped, the set-up motor 46can be operated to preselect the direction of operation and the numberof revolutions to be made by the motor 10 during its next subsequentopcrating period. Although a rheostatic control system has been shownforcontrolling the acceleration and speed .of the screw-down motor, it willbe understood that a variable voltage system can be used if desired. Ita variable voltage system is used, the cut-outs 48 and 52 preferablywould control contactors or relays associated with the supply generatorfield to control the direction .and speed of the screw-down motor.

Having thus described our invention, we claim:

1. An electric motor and control system combination for controlling andindicating the next stopping position of a member drivable by a motor todifferent selected positions,successively, and comprising a motor, amember connected to the motor so as to be driven thereby to differentpositions, a control device including a movable settable means having aneutral position and movable, in one direction, while the motor is notoperating, to different preselected set positions spaced from saidneutral position, connecting means operatively connecting said movablesettable means to said motor for driving said movable settable meansfrom the position preselected while the motor was not operating, in anopposite direction toward said neutral position upon the next succeedingoperation of said motor, said control device also including meansrendered operative when said movable settable means reaches said neutralposition to stop said motor, whereby the position to which said memberis to be moved by said motor during the next operating period of themotor is preselected prior to the said next operating period, anindicating means, coupling means operatively coupling said indicatingmeans to said movable settable means so that said indicating means isdriven in fixed relation to said movable settable means, when themovable settable .means is driven in said one direction, to a positionwhich nchcates the final predetermined position to which the member willhave been driven upon completion of said next operating period of themotor, and means rendering .said coupling means inoperative when saidmotor is driving said movable settable means in said opposite direction,toward its neutral position, and concurrently is driving said membertoward said final predetermined position.

2. A control system and motor combination in accordance with claim 1characterized in that said motor drives said movable settable meansthrough a difierential gear having its main driving gear connected tothe motor, and said indicating means is coupled to one of the outputshafts of the differential gear, and said movable settable means iscoupled to the other of the output shafts of the diiferential gear.

3. A control system and motor combination in accordance with claim 1characterized in that said movable settable means is movable selectivelyin opposite directions from said neutral position, said motor isreversible, and means associated with said control device determines thedirection of operation of said motor during its next period of operationdepending upon the direction said movable means is moved from saidneutral position.

4. A control system and motor combination in accordance with claim 1characterized in that said control device 10 includes means forcontrolling the speed of said motor and rendered operative to reduce thespeed of said motor when said movable means nears said neutral position.

5. A control system and motor combination in accordance with claim 4characterized in that said speed controlling means includes one controlmeans for controlling said motor during high speed operation of saidmotor, another control means for controlling said motor during slowspeed operation of said motor, and means for transferring from said onecontrol means to the other after said motor has slowed down.

References Cited in the file of this patent UNITED STATES PATENTS

